1. Field of the Invention
The present invention relates to an improvement in or relating to an induction-heating bender which can bend metal workpieces of different cross-sections while being induction-heated.
2. Description of Related Art
A conventional induction-heating bender comprises a pivot arm for holding a metal workpiece to be bent and an induction-heater in the form of high-frequency coils, which are adapted to encircle the metal workpiece. The metal workpiece is heated and softened, so that it may be bent by applying a bending forth to its end with the pivot arm. In case that selected sections of an elongated beam-like workpiece are bent sequentially to provide different curvatures thereover the effective radial length of the pivot arm is changed for each selected section. The induction-heater has coolant nozzles formed on the inner surface of the induction coil. Thus, required cooling is effected at same temperature irrespective of which parts of the metal workpiece being subjected to compression or stretch.
The conventional induction-heating bender can bend beautifully a beam-like metal workpiece at same curvature. An elliptical bending or spiral bending, however, cannot be beautifully performed; transitions between different curvatures show unpleasing appearance.
The cooling at same temperature irrespective of which parts of the workpiece are compressed or stretched is likely to cause wrinkles or ridge-like projections to appear on the metal workpiece, such as an H-crosssectioned steel as seen from FIG. 13. Also, disadvantageously a noticeable amount of stress remains in a certain workpiece of large cross-sectional coefficient such as an H-crosssectioned steel. Such a metal workpiece cannot be bent with precision, and the so bent article has poor mechanical characteristics.